Atrial fibrillation is a common cardiac condition in which irregular heart beats cause a decrease in the efficiency of the heart, sometimes due to variances in the electrical conduction system of the heart. In some circumstances, atrial fibrillation poses no immediate threat to the health of the individual suffering from the condition, but may, over time, result in conditions adverse to the health of the patient, including heart failure and stroke. In the case of many individuals suffering from atrial fibrillation, however, symptoms affecting the patient's quality of life may occur immediately with the onset of the condition, including lack of energy, fainting and heart palpitations.
In some circumstances, atrial fibrillation may be treated through the application of defibrillation shocks. In cases of persistent atrial fibrillation, however, surgery may be required. A surgical procedure originally developed to treat atrial fibrillation is known as a “MAZE” procedure where the atria are surgically cut along specific lines and sutured back together. While possibly effective, the MAZE procedure tends to be complex and may require highly invasive access to the thorax. In order to reduce the need to open the atria, thermal ablation tools were developed to produce lines of inactive heart wall that mimic the MAZE procedure. Such ablation tools commonly utilize radio frequency (RF) ablation devices to ablate and isolate tissue which may be responsible for the improper electrical conduction that causes atrial fibrillation. One such location of tissue which may be responsible for improper electrical conduction is at the junction of the pulmonary veins with the left atrium where spontaneous triggers for initiation of atrial fibrillation have been found. Patients who suffer from a paroxysmal form of atrial fibrillation experience short, self terminating episodes of atrial fibrillation. “Lone” atrial fibrillation occurs in patients who have either few or no other significant cardiac diseases.
Access to the left pulmonary veins by an inferior approach may be relatively free from interference. However, ablation around the right pulmonary veins may be relatively more complicated due to the presence of the superior and inferior vena cava as well as by pericardial tissue called a pericardial reflection. Pericardial reflections stretch from the right pulmonary veins to the superior vena cava, from the right pulmonary veins to the inferior vena cava, and the right superior pulmonary vein the left superior pulmonary vein. These pericardial reflections may effectively block any ability to surround the right pulmonary veins so as to ablate tissue in and around the right pulmonary veins without first dissecting at least one, and generally two, of the pericardial reflections to physically permit access to an ablation device. Pericardial reflection dissection may be undesirable under minimally invasive access. A procedure requiring dissection of the pericardial reflections may significantly increase the time required to do the overall procedure and increase the risk of unintended tearing or perforation of the heart or extracardiac structures. Moreover, while the right pulmonary veins may be accessible from the inferior side of the heart, by a sub-xiphoid access procedure, the presence of the inferior vena cava may make the ability to clamp an ablation device on the right pulmonary veins difficult or impossible without constricting the flow of blood through the inferior vena cava.